Duplexer with phase shifter circuit

ABSTRACT

A duplexer comprising an improved matching circuit for matching between transmitting path and receiving path is specified. In this case, the matching circuit comprises a hybrid and matching elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. 102012 107 244.2 filed on Aug. 7, 2012, the disclosure of which isincorporated herein by reference in its entirety.

DESCRIPTION

The invention relates to duplexers, e.g. for mobile communicationdevices, which comprise a phase shifter circuit in order to matchimpedances of transmission and reception signal paths.

Duplexers usually comprise a transmitting filter in a transmissionsignal path and a receiving filter in a reception signal path. Ingeneral, it is not readily possible to interconnect these two filtersdirectly with a common terminal, e.g. an antenna terminal. Therefore, induplexers a matching circuit is usually provided between transmittingfilter and receiving filter. A matching circuit can consist of orcomprise a phase shifter circuit. The matching circuit increases theisolation between transmission signal path and reception signal path tovalues that fulfill predefined specifications.

US 2010/0148886 A1 discloses, for example, a duplexer comprising a phaseshifter circuit as matching element. In this case, the phase shiftercircuit comprises a 0°/90° 3 dB hybrid having four terminals. The firstterminal is interconnected with an antenna, while the fourth terminal isinterconnected with the transmission signal path. Terminals two andthree are in each case interconnected with a balanced guided line of thereception signal path.

It is desirable to be able to choose from a large number of duplexers inorder to be able to comply with specifications regarding the isolationthat are applicable nowadays or in the future.

It is therefore an object of the present invention to specifyalternative duplexers comprising phase shifter circuits. It is anobject, in particular, to specify duplexers having improved, i.e.increased, isolation between transmission signal path and receptionsignal path.

This object is achieved by means of the duplexer according to claim 1.In this case, dependent claims specify advantageous configurations ofthe invention.

A duplexer that fulfills these objects comprises an antenna port, atransmitting port and a receiving port. The duplexer furthermorecomprises a hybrid interconnected with the antenna port, thetransmitting port and the receiving port. The duplexer furthermorecomprises a transmitting filter in a transmission signal path betweenthe hybrid and the transmitting port. A receiving filter of the duplexeris interconnected in a reception signal path between the hybrid and thereceiving port. In this case, the reception signal path comprises twoconductor sections connected in parallel. A matching element isinterconnected between the transmitting port and the hybrid and/orbetween the receiving port and the hybrid.

In this case, the hybrid and the matching element constitute the phaseshifter circuit of the duplexer. A hybrid within the meaning of theinvention can in this case be an RF power divider circuit having fourterminals. One port of the hybrid can furthermore be interconnected withthe transmitting port. A further port, e.g. a third port, can in thiscase be interconnected with an antenna path of the duplexer and beprovided for distributing received RF signals between a second port anda fourth port. In this case, there can be a phase difference betweenthese two output signals. These two ports two and four can then beinterconnected with the receiving port of the duplexer.

It has been discovered that the provision of a matching element in thephase shifter circuit can drastically improve the isolation of theduplexer.

In one embodiment, the duplexer correspondingly comprises a hybridhaving a first, second, third and fourth port. The first port is aninput port and can be interconnected e.g. with the transmission signalpath. The second port and the fourth port can be an output port of thehybrid, wherein there is a phase difference of approximately 90° or ofapproximately 180° between output signals of the second and fourthports.

A so-called balanced/unbalanced duplexer can be obtained with such amatching circuit comprising a hybrid. In this case, the reception signalport can comprise balanced guided signal lines interconnected with thehybrid. Balanced guided signal lines have a significantly lowersusceptibility toward common-mode interference. The hybrid having thetwo output ports two and four in this case constitutes a simple buteffective measure for dividing unbalanced guided RF signals originatingfrom an antenna between the two balanced guided signal lines of theunbalanced/balanced duplexer.

In one embodiment, the reception signal path is correspondingly providedfor guiding balanced guided RF signals.

In one embodiment, the duplexer comprises a matching element inparticular between the transmitting port and the transmitting filterand/or between the transmitting filter and the hybrid. The matchingelement can be the abovementioned matching element or a further matchingelement.

The matching element can comprise, in particular, a stripline orcapacitive or inductive circuit elements.

In one embodiment, the duplexer comprises a matching element between thehybrid and the receiving filter and/or between the receiving filter andthe receiving port. In this case, the matching element can in turn bethe matching element mentioned in the introduction or else an additionalmatching element.

In one embodiment, the matching element is, in particular, a capacitiveelement, an inductive element or a stripline. The matching element canalso comprise an interconnection with a capacitive element, an inductiveelement or a stripline.

In one embodiment, the transmitting filter and/or the receiving filteroperate(s) with acoustic waves. In particular, components operating withsurface acoustic waves (SAW), with bulk acoustic waves (BAW) or withguided surface acoustic waves (GBAW=Guided Bulk Acoustic Waves) areappropriate as filters.

There are filters operating with acoustic waves and having intrinsicbalun (balanced/unbalanced transformer) functionality. Such filters are,for example, so-called DMS (DMS=Double Mode Surface Acoustic Wave)filters. The provision of a hybrid for generating output signals havinga phase difference in this case makes it superfluous to use suchrelatively complex and therefore generally expensive components. Inparticular the use of CRF (CRF=Coupled Resonator Filter) operating withBAW (BAW=Bulk Acoustic Wave) or the use of further balun circuits can bedispensed with.

In one embodiment, the hybrid comprises coupled transformers. In thiscase, such a hybrid comprises coils or windings that areelectromagnetically coupled to one another. The number of windings ofthe coil which is interconnected with a respective one of the terminalscan be set individually in this case. It is thus readily possible to setthe impedance level of each individual terminal. Particularly if thereception signal path and the transmission signal path are galvanicallyisolated by the provision of coupled transformers in the hybrid, veryhigh isolation values are obtained.

Furthermore it is possible in a simple manner for the output of thehybrid that is interconnected with the transmission signal path to bedesigned with low impedance.

The turns ratio of the coupled transformers can be 0.5. Thus, theimpedance of the transmitting port can be set to 25 ohms, the impedanceof the two balanced guided signal lines of the receiving port can be setto 100 ohms and the terminal of the hybrid that is interconnected withthe antenna can be set to 50 ohms.

Duplexers comprising phase shifter circuits are explained in greaterdetail below on the basis of exemplary embodiments and associatedschematic figures. In this case, different figures illustrate differentaspects of the invention, which, of course, are not mutually exclusivebut rather can be combined with one another.

In the figures:

FIG. 1 shows: a configuration of a duplexer comprising a transmittingport TP, a receiving port RP and a hybrid H between the transmittingport and the receiving port,

FIG. 2 shows: a configuration of a duplexer, wherein matching elementsME can optionally be provided,

FIG. 3 shows: a configuration of a duplexer comprising two balancedguided signal lines between hybrid H and receiving port RP,

FIG. 4 shows: the configuration of a duplexer whose hybrid H operateswith coupled transformers,

FIG. 5 shows: a T-circuit with resonators,

FIG. 6 shows: a Π-circuit with resonators,

FIG. 7 shows: the insertion losses of the transmission signal path (TX)and of the reception signal path (RX) and also the isolationtherebetween for a configuration of a duplexer,

FIG. 8 shows: insertion losses and isolation for one particularlyadvantageous embodiment of a duplexer.

FIG. 1 shows an embodiment of a duplexer DU comprising a transmittingport TP, an antenna port AP and a receiving port RP. A transmittingfilter FTX is interconnected between the transmitting port TP and theantenna port AP. The signal path from the antenna port AP to thereceiving port RP is embodied as balanced and thus comprises two signallines connected in parallel. A receiving filter FRX1, FRX2 isinterconnected in each of the two signal lines. A matching element ME isfurthermore interconnected in the signal line in which the receivingfilter FRX1 is interconnected. Consequently, the receiving filters FRX1,FRX2 and the matching element ME are interconnected between the antennaport AP and the receiving port RP. Furthermore, a matching element ME isinterconnected between the antenna port AP and the transmitting port TP.The interconnection of receiving port RP, transmitting port TP andantenna port AP is effected via a hybrid H. The hybrid H has four portsor terminals. Via a first terminal, the hybrid H is interconnected withthe transmitting port TP. Transmission signals are conducted from thetransmitting port TP into the hybrid 1. Consequently, the first terminalof the hybrid is an input port. Signals received by the antenna aretransmitted via the output ports two and four of the hybrid to thereceiving port RP. The third port of the hybrid is interconnected withthe antenna port AP. The hybrid H brings about a phase differencebetween the output signals present at the ports two and four of thehybrid H, such that balanced guided signals are present at the receivingport RP. If the hybrid H is a 90° hybrid, then the matching element MEbetween the receiving filter FRX1 and the receiving port RP can carryout a further phase rotation by 90° such that a phase difference ofsubstantially 180° is present at the receiving port RP. If the hybrid Halready provides a phase difference of 180° then there is no need for afurther phase rotation in the reception signal path.

FIG. 2 shows an embodiment of a duplexer, wherein additional matchingelements ME can optionally be interconnected in the signal paths. Amatching element ME can be interconnected between the transmittingfilter FTX and the transmitting port TP. A further matching element MEcan be interconnected between the fourth port of the hybrid and thereceiving filter FRX1. A further matching element ME can beinterconnected between the second port of the hybrid and the receivingfilter FRX2. The matching element ME between the receiving filter FRX1and the receiving port RP is also optional, as is the matching elementME between the receiving filter FRX2 and the receiving port RP.

The hybrid in FIG. 2 can be, in particular, a 90° hybrid.

FIG. 3 shows a configuration of a duplexer DU, wherein the hybrid can bea 180° hybrid. The hybrid H has a first port, via which it isinterconnected with the antenna port AP. Via its second port, the hybridH is interconnected with the transmitting filter FTX between hybrid Hand transmitting port TP. Via its third port, the hybrid H isinterconnected with a first signal line of the balanced guided receptionsignal path. With its fourth port, the hybrid is interconnected with thesecond signal line of the reception signal path. In the first signalline of the reception signal path, a receiving filter FRX1 is arrangedbetween two matching elements ME. Alongside the receiving filter FRX2,the second signal line of the reception signal path can comprise furthermatching elements, e.g. between the hybrid and the receiving filter FRX2or between the receiving filter FRX2 and the receiving port RP.

FIG. 4 shows a configuration of a duplexer DU, wherein the hybrid Hcomprises coupled transformers, e.g. two coupled transformers. Thecoupled transformers in each case comprise electromagnetically coupledwindings or coils. Thus, one terminal of a coil can be interconnectedwith a first port of the hybrid H, while the respective other terminalof the coil is interconnected with the second port of the hybrid H. Oneterminal of the coil coupled to said coil is interconnected with thethird port of the hybrid H, while the other terminal of the coil isinterconnected with the fourth port of the hybrid H. It is possible forthe second port of the hybrid H to be interconnected with ground. Thefirst port of the hybrid H is interconnected with the antenna port AP.The fourth port of the upper coupled transformer and the third port ofthe lower coupled transformer are interconnected with the transmittingpath TP. The third port of the upper coupled transformer and the fourthport of the lower coupled transformer are in each case interconnectedwith the balanced guided signal lines of the reception signal path andthus with the receiving port RP. Once again, a respective receivingfilter FRX1, FRX2 is interconnected in each of the reception signallines of the reception signal path. Moreover, these signal lines cancontain matching elements ME between the hybrid and the correspondingreceiving filter FRX1, FRX2 or the corresponding filter and thereceiving port RP.

FIG. 5 shows a basic form of a filter comprising resonators, whichfilter can be used for example as a transmitting filter. In this case,FIG. 5 shows a so-called T-circuit comprising resonators.

FIG. 6 shows a so-called π-circuit comprising resonators, which canconstitute, in particular, a basic element of a receiving filter.

The resonators of the filters in FIGS. 5 and 6 can in this case beresonators operating with acoustic waves, such as SAW resonators, BAWresonators or GBAW resonators.

FIG. 7 shows the insertion loss IL_(TX) of the transmission signal pathand the insertion loss IL_(RX) of the reception signal path.Furthermore, curve IS shows the isolation between transmitting port andreceiving port. FIG. 7 in this case shows characteristic curves of aduplexer comprising a matching circuit, wherein a hybrid isinterconnected in the matching circuit.

FIG. 8 shows the corresponding curves of the insertion losses and theisolation IS of a duplexer comprising a particularly powerful matchingcircuit. In this case, the isolation is substantiallyfrequency-independent and better than −160 dB over the entire relevantfrequency range. Such an insertion loss also appears to be able tocomply well with future specifications.

The excellent performance of the duplexer, the characteristic curves ofwhich are shown in FIG. 8, is based in this case on the use of coupledtransformers in the hybrid.

A duplexer according to the invention is not restricted in this case toone of the exemplary embodiments described. Combinations of describedfeatures and variations which comprise e.g. even further matchingelements likewise constitute exemplary embodiments according to theinvention.

1. A duplexer, comprising: an antenna port, a transmitting port and areceiving port; a hybrid, interconnected with the antenna port, thetransmitting port and the receiving port; a transmitting filter in atransmission signal path between the hybrid and the transmitting port;and a receiving filter in a reception signal path between the hybrid andthe receiving port, wherein the reception signal path comprises twoconductor sections connected in parallel, and wherein a matching elementis interconnected between the transmitting port and the hybrid orbetween the receiving port and the hybrid.
 2. The duplexer according toclaim 1, wherein the hybrid comprises a first, second, third and fourthport, and wherein the first port is an input port and a phase differencebetween output signals of the second and fourth ports is approximately90° or approximately 180°.
 3. The duplexer according to claim 1 or 2,wherein the reception signal path is provided for guiding balanced RFsignals.
 4. The duplexer according to claim 1, further comprising amatching element between the transmitting port and the transmittingfilter or between the transmitting filter and the hybrid.
 5. Theduplexer according to claim 1, further comprising a matching elementbetween the hybrid and the receiving filter or between the receivingfilter and the receiving port.
 6. The duplexer according to claim 1,wherein at least one matching element is selected from: a capacitiveelement, an inductive element, a stripline.
 7. The duplexer according toclaim 1, wherein the transmitting filter or the receiving filteroperates with surface acoustic waves, with bulk acoustic waves or withguided bulk acoustic waves.
 8. The duplexer according to claim 1,wherein the hybrid comprises coupled transformers.
 9. The duplexeraccording to claim 8, wherein the turns ratio of the coupledtransformers is 0.5.
 10. The duplexer according to claim 1, wherein theantenna port has an impedance of 100 Ω, the transmitting port has animpedance of 25 Ω and the receiving port has an impedance of 100 Ω.